Electroplating process



June 4', 1940. BROWN 2,203,253

ELECTROFLATING PROCESS Filed Sept. 26, 1936 Mmvm? M BROWN I 50 aconductor Patented June 4, 1940 PATENT OFFICE 2,203,253 ELECTROPL ATINGPROCESS Morris Brown, La Grange, em Electric Company, Incorporated,

111., assi'gnor to'west- New York,

N. Y., a corporation of New York AppIieation SeptemberZG, 1936, SerialNo. 102,696

1 Claim.

This invention relates to electroplating processes, and-moreparticularly to the manufacture of sheet metal by electrodeposition. Themanufacture of certain metal articles, such as tubes or foil, byelectrodeposition processes, has been restricted by the tendency of themetal to adhere to the mandrel or mould on which it is deposited. In theproduction of foil by this method, the tension required to remove'thefoil 10 from the mandrel has limited the minimum thickness and also thecomposition of the product. Coatings of grease, tin, zinc or mercuryamalgam have been applied to the mandrel to overcome this'difliculty butsome of these expedients do not 15 give entirely satisfactory resultsand all of them are further objectionable in that they require periodicreplacement.

Objects of this invention are to provide improved methods and apparatusfor the efficient 20 electrodeposition of metal..

In accordance with one embodiment of the invention, apparatus isprovided for the continuous manufacture of metal foil byelectrodepositing the metal on a chromium'coated rotating mandrel, andstripping the deposited metal from the mandrel in the form of acontinuous sheet.

A complete understanding of the invention may be had from the followingdetailed description taken in conjunction with the appended drawing, inwhich Fig. 1 is a' se'chematic view, partly insection, of anelectroplating apparatus, embodying the invention;

Fig. 2 is a section of the apparatus shown in 35 Fig. 1, taken on theline 2-4, and

Fig 3 is a sectional view taken. on line 3-3 of Fig. 2. l

Referring now to the drawing, a conventional continuous electroplatinginstallation comprises a cylindrical drum or mandrel it) which isrotatably mounted on a shaft ll over a tank or container l2. The tank.is lined with lead I3 and contains an electrolyte ll of suitable metalsalt in which the mandrel is partially immersed. In accordance with wellknown practises, plating "current of suitable characteristics issupplied from a battery l5 or other source with its negative terminal l6connected to the mandrel or cathode through a sliding contactor I'lengaging i8 which is imbedded in insulation in the mandrel shaft andconnected to the mandrel through a wire 19. The positive terminal 20 ofthe battery is connected directly to the lead sheet lining of the tankwhich serves as an inu soluble anode.

'Ihe'electrolyte is circulated through, the'tank against the rotatingmandrel by a pump or other suitable. means (not shown). The tank has arounded bottom approximately conforming with the mandrel contour.Depleted electrolyte is 5 withdrawn from one end of the tank,replenished with metal salt in an external apparatus, (not shown) andrecirculated. The metal deposited on the rotating mandrel is strippedfrom the mandrel surface in the form of a continuous sheet or foil 2| bya revolving takeup spool 22 supported in bearings 23 over the mandreland driven through a belt 24 by suitable and conventional mechanism (notshown) for applying a constant tension to thefoil.

The general features of the apparatus and process so far described areold and well known and this invention is directed primarily to theconstruction of the mandrel on which the metal is deposited. Thepreferred construction is particularly suitable for the production ofcopper foil ,under .0093" thick which is useful in the manufacture ofcondensers and other products. Foil used for this purpose must beuniform in thick? ness and preferably has a smooth, continuous sur- 25face.

It is possible to control 'the thickness of the deposited sheet ingeneral by regulation and coordination of the plating current,electrolyte composition, mandrel size and operating speed. However,copper in this dimension possesseslittle' tensile strength and even veryslight tendency of the foil to adhere to the mandrel results inbreakage. It is undesirable to use temporary coatings of foreignsubstances on the mandrel surface to reduce sticking of the foil becausethe deposited metal conforms rigidly to the contour of the mandrel andreproduces any surface irregularities. It is difficult to apply thesecoatings I smoothly and their repeated use may destroy the 40 surface onthe mandrel.

To overcome these objections, the mandrel is provided with a permanentlysmooth, uniform surface from which the deposited metal can be readilyremoved. The mandrel comprises a steel cylinder 25 (Figs. 2 and 3) whichis formed to v shape and ground on the outside surface to re-. move allirregularities and imperfections. Other materials can be used for thismember, but steel is preferred because of its stability in retaining thesurface and shape produced in the grinding operation. A layer of nickel26 is plated unlformly on the ground surface of the cylinder andsubsequently buffed to a high polish. A nickel coating .0005" thick issatisfactory for most inpolish. This coating may alsovary inthickness,

but coatings around .00005" thick give good results.

The composite mandrel cylinder is supported at each end by a disk shapedmember '28 made of wood, fiber, or other insulating material and securedto the mandrel shaft. At each end of the mandrel cylinder, a-ring 30made of rubber or other insulating material is imbedded in the peripheryof the disk. The ring projects above the surface of the mandrel to formthe deposited foil with uniform, unbroken edges. g

The side of the foil next to the mandrel-has a smooth surface,determined by the finish on the mandrel, but the other side may bespongy or rough. To smooth this outer surface, a roller 3| is rotatablymounted parallel to the mandrel in' bearings 32 in contact .with thefoil on themandrel surface. The roller is driven from the man drel shaftthrough a twisted belt 33 engaging pulleys on the mandrel and rollershafts. pulleys are selected to rotate the rollerat a surface speedapproximately 15% higher than the surface speed of the mandrel whichproduces a burnishing action and imparts a smooth polished surface tothe foil. The relative surface speeds of the roller and mandrel may bevaried for different foil thicknesses and compositions arid undervarious conditions the roller mayoperate at speeds from 10% to higherthan the 'mandrel. The position of the burnishing roll is madeadjustable relative to the mandrel by any suitable means (not shown) andthe roll is located to control the final thickness dimension of thefoil.

In the operation of the process, the chromium, being passive, preventsadherence between the foil and mandrel. As a result the foil is readilyremoved with a slight takeup tension which preited metal.

The

vents damage to the product ariddacilitatesthe manufacture of thinnerfoil. It is also possible with this'apparatus'to produce-foil frommaterials having relatively. low tensile strengths, such as gold ornickel. 1

A mandrel constructed in accordance with the above description is alsosuitable for. the manufacture of tubes or'shapes. In this process-,themetal is plated on the mandrel, which may be stationery or rotating,after which 'the mandrel is readily withdrawn from the completedarticle.- If desired, the chromium can be plated directly on'the steelcylinder to provide a mandrel with a passivesurface that will not adhereto the depos- However, the intermediate layer of nickel is beneficialasit facilitates the application of the. chromium and the development'of asmooth uniform surface. A mandrel formed entirely of chromium willoperate satisfactorily, butv the composite mandrel is more serviceableand less costly.

Other adaptations and modifications of the specific embodiment abovedescribed are feasible and it is to be understood that the inventionislimited only by the scopeof the appended claim.

I Whatis claimed is: -A method of producing thin compriseselectrodepositing" a copper layer less than .0003" in thickness on achromium surface while said surface is moving at a predetermined speed,compressing 'the deposited copper against the chromium surface by meansof a cylinder having a metallic surface maintained a fixed distance fromthe chromium surface to size the copper into foil of -a'predeterminedthickness, withdrawing the foil from the chromium surface with apredetermined tension around an arc of said cylinder, and rotating thecylinder at a surface speed from 10% to- 25% higher than the copper foil.which speed of the chromium surface to polish the foil in the arc ofcontactwith said cylinder.

MORRIS BROWN. I v

